A Navy blimp has been in flight over the city since last month, as a contractor tests its sensors to see how well they will work for mapping.

Doug Abbotts, a spokesman for the Naval Air Warfare Center Aircraft Division said the 178-foot blimp’s trek, which was scheduled to end Saturday, was funded through a contract his agency made with the Army earlier in the year.

As long as the contract is in place, the blimp will continue its voyage.

"There's no money from Congress going into this," Abbotts said.

Over the course of the week, people have been asking on social media about why the craft hadn't been grounded by the impasse over the federal budget.

"Despite the #shutdown, this Navy blimp is still mapping #Baltimore. What gives?" Twitter user Sharon Paley wondered on Wednesday.

The answer points to the complexity of federal spending -- shutdown or no. The Naval Air Warfare Center has been able to continue operations because it is what's known as a "working capital fund organization" that gets no direct funding from Congress.

Abbots said his division sustains itself through contracts with other government agencies.

Similar organizations, which exist throughout the federal government, are funded through special arrangements made with the U.S. Treasury, said Cmdr. Bill Urban, a U.S. Department of Defense spokesman.

Other government groups function through a combination of working capital funds and congressional finances.

"They have money remaining in their accounts from a multiyear appropriation," Urban said.

As of Oct. 1, approximately 150,000 Department of Defense civilian employees were able to continue working during the shutdown thanks to working capital funds. But, Urban warns, their days are numbered as the funds become depleted.

Urban did not have an estimate for how many such organizations there are.